Direct current amplifier and method of operating same



Sept. 12, 1933. F, WA Z 1,926,568

DIRECT CURRENT AMPLIFIER AND METHOD OF OPERATING SAME Filed Feb. 21, 1930 a' mmm l INVENTOR QQMAW ATTORNEY$ Patented Sept. 12, 1933:

. "DIRE'oToURRENr AM LIFIE YAND 1 .METHOD or or m'rruo. SAME, j

Frank OeWalz, BouldenColoL, assignorrof "on'ehalf' to Stanolind Oiland Gas Company I 'iTulsa, kla., acorporationof Delaware a 3 App lieation February 2.1,193thSeriallqoi lmtl'l .7 Claims. (Cline- 171 V The invention relates to directcurrent amplifiers, which include. an electron discharge device or audion, with a resistance; inthe grid circuit bridging the input terminals or leads-and hastf or its object to compensate the potential drop across said resistance, so that the points of connection of the external-circuit on, opposite sides of the a resistance are at the same-potential, whereby the readings of avoltmeter, galvanometer or similar ,indicato'r, includedintheoutput circuit, will be i directly proportional toQthevoltages of any external circuit with which the amplifier is con- ,nected and arefindependent of the resistance of such external-circuit. 7

Various modes of applying the invention are illustrated in the accompanying drawing, in

which:--

Fig. l is adiagramiora, iying systemfor use with avoltmetenembodyin .fied "meanshfor compensating; the voltage drop the resistanceyelement of the grid circuit. .The most.- practical and .widely' used circuit .ior leads, adaptedto be connected @to the; external cuit-of the audion or'electron; deviceawhi'ch redirect current'amplifier is the measuringof volthigh input resistance and also high amplification, it is necessary to have the resistance in the grid'circuit of nearly'the same magnitude as the resistance in the circuit from the grid to the filament of the first tube or audion.

have zerogrid current, it is obvious that there will be a potential drop across the resistance in 1-3450 the grid circuit. The measure of this drop in the potential or voltage will be indicated a'pproXi-.

or zero resistance. there would large change i rect current ampli- .resistance-is much larger than .13118 "preferred [form of, theinvention r :2 I Figs, 2and f3 are;.sirni1ar views showing modiarrangement iO \;the- -input of a direct; current I amplifying system includes the input --.terminals ages to be indicated by ;a meterincluded in the output circuit, and. a necessary; characteristic of such a meter is thatit involves .a high resistQ-j ance, in' fact, the magnitude of the resistance per I volt measured by the meter ismore or less an index or. its worthi and efficiency; In an appa- 1 ratusof the kind'referred to, in order to obtain;

in potential or thegrid and; an -equa e,- i a large change in theplatecurrentli For the case r in. which the input circuit isshorted, the ngage in the grid voltage would be approximately RIg.

Inasmuch assucha change in voltage would be from 1000' to 10000 times the range of potential which-an amplifier would-be designed to measure, it is obvious that disastrous effects .onthe gal-.

vanometer or voltmeter employed in the output circuit andflalso onthe outputaudion or. tube 5.

, (if more than one stage of amplificationwere f .used), would ensue It is, therefore, apparent that the ordinary input of adirect current amplifier is unsuited for opencircuit work and, also, that thegzero settingot the amplifier is dependent 0 upon the resistance of the external circuit to which the amplifier. is connected, unless, that the resistance included in the gridcircuitq I ..The present invention is designed to adapt the direct currentamplifierof thetype indicated to the measurementsof voltages in-an ex- .ternal circuit wholly independent oof the resistance in said circuits and depends primarily, upon the principleof establishingpoints of equal po. ,3 tential between :the input-terminals or leads on r opposite sides of the resistance in the grid circuit circuit and :a resistancejincluded 11111116 grid cir- I \;"A- relatively simple method of obtaining this result is exemplified in Fig. 1, in which hand 2 plifier by a. voltmeter, 'galvanometer or the like included. in the output circuit of the amplifier. -Az indicates atypical audion or tube,Eg the battery-included-in the grid circuit, which latter includes :a resistance R, which: bridges the input terminalsor .leads and which, therefore, im- -poses a difference of potential on the input terminals, which must} be compensated for or balanced out, if the apparatusiis tobeefiective for V terminals. As indicated in the diagram, the drop in potential across the resistance R. is 'compenlilo y, sated by including'one of the cells of the grid Since it is impossible to design tubes which f battery'Egi across the input terminals-or leads, so that the voltage of said cellwill compensate for. the drop'in voltage across the resistance R r andihis compensating voltage is accurately reg-T 0 vulated by means of the slide-S connecting the input terminal 1 with the resistance B, said sliding contact being adjustable with respect to the resistancejR. It will, therefore, be seen that the is now included between "the input terminals. This makes it possible toadjust thepotential drop across R equal to the potential rise of the cell, so that the rise in potential cancels thedrop in potential, and, therefore, obtains or establishes zero potential difference between the input terminals. Before connecting the external circuit,

"the, zero potential difference therebettveen can: readily be determined and established by closing the tap key K bridged ibetweenthe input terminals and adjustingthe slide S until no dethejamplifier readings indicatedron the'meter G will be strictly proportional to thevoltages in the external circuit connected to the inputiterminal's 1 and are holly independent of the resistance of such'circuit, "Inasmuch asth 'eigrid currents are" *egrtremely small, vith the usual negative grid biasfthe resultant drain on the grid battery is also small; wherefore the current is very steady ,and' one adjustment'of the apparatus .should suffice-for manyhours of use,

In the modified form ofthea'pparatusillustrated infFig; 2,i practically the only difference is thatthe countervailing voltage from the grid 1 means of-a shunt about the grid-batteryEgQin "which-i's-included a resistance"R"and a sliding contact S"associated therewith, so that the' voltage between'fpoints a anewmay be accurately "adjusted to exactly compensate forthe drop'of voltage duet'o'the r'esistance*R.-* Fig. 3'shows a furtherlmodificationin whic'h'a,

separate cell orbattery E,togetherwith an adbattery to the input terminals is obtained :by

justableres'istanceR and fan adjustableslide S cooperating Withsaid resistance, is included between'the input terminals or leadsin the manner I and form shown, the slide S' being adjusted "until points-awandb are at the same potential.

In each form o'f the apparatus, thecompensating voltage imposed onthe inputt'ermi'nals or' leads is so regulated, asto equal the'drop of ipotential across .the' resistance Rfin -the grid -circuit,}r,:as indicated intFig. 1, to establish equal-potentials at points a and!) in theinput' circuit, on opposite sides of theresistance and,

litf j laninput coupling resistance in the grid circuit the points beforethe external connections'a'r' made and this is effected by imposing an electromotive force or potential drop on the input leads circuit to compensate forthe drop in potential across the resistance.

' What I claim is:

V1. The method of compensating the potential drop caused by the flow of grid current through of a direct current amplifier, which comprises imposingi a potential difference upon the input circuitof the amplifier in opposition to the poten-' "tial drop 'acrosstlie resistance, and; regulating said; imposed potential differences to compensate the total potential drop; whereby the voltage of the output" circuit with which the amplifier isas'sociated Will not be affected'by the flow of gridicurrent in the amplifier.

. 2; The method; as described in claiml, in

which the potential difference isderive'd from a portion of the grid circuit current source;

13. In a'voltage measuring system, comprising potential in the opposite sides of the'inputcirf cuit, whereby; the; voltage of the output circuit with which thejamplifie r is associated will be directlypr'opertional to "the voltage of the input 1 "circuit; 1 r

4. Anzaudion amplifying circuit, including an initial audion amplifier and a resistance inbridgingre'lation with "the input circuit, 'meansfor compensating the total. voltage drop across said resistance; comprising a source of potential connected '00 the input circuit in oppositionto the normal potential across; said resistance,- and means for-regulatingthe said source of potential l whereby the voltage of the output: circuit with 1 which the amplifier is. associated will be direct-- 1y proportional-to'the voltage-of the'input circuit.

5 An audion amplifying-circuit including an in- "itial audion amplifier and a resistance. in bridgv ing relation with the input "circuit, means 'for similarly, a and b inFig. 2, and aand-11" in Fig. 3. The balancing of the potential differ-- ence is with respect to theext'ernal circuit only,

' I and not the grid circuitfas the normalvalue of the "grid potentialfremains 'unaltered.- The: gen

'eral principle involvedin the practice 'of thexin 'vention is to connect 'theinput' leads toany two points on opposite sides of the resistance in-the grid circuit in such manner'that the pointsare at the same potential; that is to say, there is no a normal differenceof potential existing between compensating the total. voltage drop across said resistance including? a portion of the gridicircuit p'otentialflsource' connected to the input cir- (nut in opposition to-the normal'potential inthe. j

grid circuit, and means for regulating the o'pposition potential, whereby the voltage of the out- Ami cQy V LZI. 

